1. Field of the Invention
The present invention relates generally to audio loudspeakers. More particularly, the invention relates to a loudspeaker system that simulates the complex directional radiation patterns of sound. The directional radiation patterns, a strong function of both spacial position and frequency, produce the psychoacoustic illusion that the reproduced sound comes from the original musical instrument source.
2. Description of Related Art
Pierre Boulez has observed that loudspeakers have the property of "anonymizing" the sound of musical instruments, that is, of making them all sound the same. "Le haut-parleur anonymise la source reelle." P. Boulez, Proc. 11th International Congress on Acoustics, Paris, 8, 216 (1983). Considerable effort has been expended in improving the sonic accuracy of loudspeakers and in developing stereophonic and surround sound techniques in an effort to simulate the psychoacoustic experience of "being there." Yet the objective remains elusive. The loudspeaker art has not heretofore addressed the unfortunate anonymizing property observed by Boulez.
I have discovered that the complex and widely varied radiation patterns of musical instruments provide a strong psychoacoustic cue and that the simulation of such complex radiation patterns produces a surprising realism not found in conventional loudspeaker systems. I use the solo violin to demonstrate.
Above about one kHz, the angular radiation pattern of a violin begins to vary rapidly, not only with direction but also with frequency, typically changing drastically from one semitone to the next. In an enclosed space, this characteristic, which I call directional tone color, can produce the illusion that each note played by a solo violin comes from a different direction, endowing fast passages with a special flashing brilliance. Directional tone color also has important consequences for the perception of vibrato, for the difference in sound between a solo violin and an orchestral section playing in unison, for the mysterious quality called "projection," and for the problem of reproducing violin sounds through a loudspeaker. Furthermore, directional tone color is important for the reproduction of extended sound sources which generate different notes from different locations, such as a pipe organ or an orchestra.
The present invention simulates complex radiation patterns or directivity patterns of musical instruments, resulting in a surprising realism. The invention employs plural radiators or transducers, such as individual loudspeakers, disposed in proximity to one another and individually fed by separate sound sources. More specifically, the individual sound sources each provide a different signal delay, so that the individual speakers receive the input audio signal at slightly different times. In the preferred embodiment these sound sources also incorporate attenuated feedback, so that each speaker receives the audio input signal as a decaying reverberant signal. The preferred embodiment also includes a low frequency radiator or woofer that is supplied through a low pass filter without delay.
The inter-speaker spacing and the delay times cooperate to produce a complex angular radiation pattern that varies rapidly with both direction and frequency. The individual radiators each establish individual sound fields that interact constructively and destructively to produce the complex, time-varying radiation pattern. The listener, even a stationary listener, will perceive these rapidly varying radiation patterns, due to the frequency variation of the source material and due to acoustic reflections from surrounding walls and furniture. Unlike conventional stereophonic or surround sound systems, the individual radiators are not widely separated to produce the realistic effect. Indeed, even a single speaker enclosure housing the plural radiators of the invention will produce a three-dimensional realism. Unlike conventional stereophonic or surround sound systems, there is no single "sweet spot" where the effect is most convincing. Rather, listeners can perceive the effect from virtually any position within the room. For a more complete understanding of the invention, its objects and advantages, reference may be had to the following specification and to the accompanying drawings.